24-July London’s Hidden Jewels: Chasing Rare Butterflies

Although they were never common, they became much rarer after the outbreak of Dutch elm disease in the 1970’s. Trent Park is still a good place to look for them as the colony there is thought to have survived the original outbreak. Another colony existed around a very rare Exeter elm in Battersea Park for at least forty years, until the park authorities, without warning or reason, cut the tree down.

Whereas white-letter hairstreaks close their wings on landing, purple hairstreaks tend to keep theirs open. This means you are never able to see the white ‘W’ marking from which it gets its name. The females of both hairstreaks are even more difficult to separate in the field, although the female purple hairstreaks are a little less purple than the males and female white-letter hairstreaks a little paler than their mates.

There are also two large fritillaries that can be seen in London in July. At the beginning of the month if one is seen it is likely to be dark green fritillary as the silver washed fritillary is only on the wing in the second half of the month. The word ‘fritillary’ means ‘dice-box’, which is a good clue to their general markings. In this case it is the habitat where the butterfly is seen which helps to identify it. If it is seen on chalk down land with woodland nearby, it is likely to be a dark green fritillary, whereas if it is seen in the wood itself, especially in a glade with tall trees, it is more likely to be a silver washed fritillary. Box Hill and Bookham Common are places you might look for both.

They fly so fast, an accurate field identification can be almost impossible. Silver washed fritillaries tend to be a reddish brown, whereas dark green fritillaries are similar but with many more dark markings. Sexing the butterflies as they hurtle past is even more difficult, although both females do tend to be a little darker than their mates. Dark Green fritillaries rarely settle for long but at Hutchinson’s bank reserve they are fond of feeding on the wild marjoram often allowing a better sighting than usual.

Although small blues are not seen this month, it is probably the best time to look for other blues i.e. common, silver studded, chalk hill, holly, Adonis and brown argus. Fortunately, they are all slightly different shades of blue. A milky or ice blue can well indicate it is a chalk hill blue. The small blue seen last month is generally the darkest blue of them all. The common, silver studded and holly blues all have some mauve or lilac tints. The silver studded is more of a leaden blue than the rest. The holly blue has such noticeable pale metallic undersides to its wings it is easily recognised.

Both male and female common blue are just a plain mauve blue. The brightest and most eye catching of them all is the Adonis blue, which has been described as a ‘brilliant, shiny sky and electric blue’. It is so memorable that it is no surprise it was named after Adonis, “the god who was as beautiful as love itself”

Fortunately, there are other characters than colour to separate blues in the field. If the butterfly is seen at rest, it is worth noting whether there is a black border to the wings or not. Also, whether the border is thin or thick or on the forewings only. The silver-studded and holly blue both have black edges, which the common blue does not. A broad, dark edge indicates a female holly blue and a thin one is likely to be a male silver studded blue. The holly blue is further distinguished by having no orange markings or bordered spots that are so typical of the other species. Its black border is just confined to the tips of its wings in the male. The females as usual are more difficult to separate, but hopefully they are not too far away from the males. The brown argus, although technically a ‘blue’, is actually chocolate in colour with orange borders.

It can look for all the world like a female common blue, but fortunately prefers to live on heaths, which the common blue does not. If you ever get near enough to a male brown argus, it is said to smell of chocolate. Good places to look for a variety of blues this month are Hutchinson’s bank, Headley Heath, Denbies hillside and the Box Hill area.

In gardens, the most likely butterflies to be seen are the comma, red admiral, peacock, possibly a painted lady and, now rarely, a small tortoiseshell. Whites can often be strangely absent this month, although the large, small and green veined do reappear towards the end of the month. The rare wood whites, where they do occur, fly the whole month. Speckled woods are even more unusual in their appearance. They may be seen at the beginning and the end of July, but not usually in the middle. When they are seen, it is worth watching out for their spiralling courtship display. This ends with the female dropping to the ground, where both butterflies start bowing to each other. The male may then wrap his wings around her antennae before attempting to copulate with her.

The other much rarer butterflies that might possibly be seen this month are the grayling, clouded yellow and purple emperor. The grayling prefers steep south-facing chalk slopes. The clouded yellow, being migratory, makes unpredictable appearances and any sighting of a purple emperor is likely to be the highlight of the month. Because of its size, beauty and unusual life history, the purple emperor is the most sought after butterfly by most naturalists. Unfortunately, they are not only both rare and elusive, but exist in low numbers when they do occur. They congregate in their mythical ’master trees’ which they use year after year. The location of these trees is usually kept a closely guarded secret, although they are often the tallest trees at the summit of the wood they have chosen to inhabit.

Here, in the high branches, they have their favourite perches where they bask, showing off their large, iridescent Tyrian purple wings. From here they occasionally then descend to chase off rivals or even human beings who are wearing bright colours. The Victorians used to employ fox dung and dead rabbits to try and lure them down from the canopy.

In the early morning, they do tend to float down to investigate any dung, especially on woodland paths. From this unlikely food source they are believed to ingest various salts that they need, consequently it is usually quite a shock when you first encounter them. Bookham Common and the ancient woods along the Surrey/Sussex border are still places to look for these butterflies, but it may be easier to persuade someone to tell you the location of a ‘master tree’.